Jim Barrow – How Cluster Roots Work

Professor Jim Barrow will speak on Cluster Roots – the amazing adaptations made by the roots of our native plants.

Many plants, and especially members of the banksia family, cope with low nutrient supply by developing cluster roots. These multi-branched regions of the root exude organic acids, especially citric acid. The way that the acidity and the citrate concentration interact to release nutrients, especially phosphate, has not been understood.

The acidity plays at least three roles. First it discourages microbial attack on the citrate so it lasts longer. Second it moves the pH into a region in which phosphate is most readily available. And third it moves the pH into a region where citrate is most effective at displacing phosphate. This is at about pH 4. At this pH, the citrate ion that is most effective at displacing phosphate is at its highest concentration.

The cluster roots enable the citrate and the acidity to be concentrated in one region but they may also keep the calcium concentration low. Calcium forms complexes with citrate and decreases its effectiveness.

Jim began his career with CSIRO in 1954, and ‘retired’ nearly 40 years later as a Chief Research Scientist. Currently, he is a Research Fellow at UWA. Jim has worked on diverse projects, but is best known for his work on mechanisms of sorbed ions in soils (phosphate, molybdate and heavy metals). The initial paper presenting a model was recently recognised by the European Journal of Soil Science as a landmark paper. The work was subsequently summarized as four laws of soil chemistry to quantitatively explain the behaviour of the reactions of cations and anions with soils.

Meetings of the Perth Branch of the Society are held on the second Tuesday of each month in the Subiaco Community Centre across the road from Crossways Shopping centre in Bagot Road. Doors open at 7.45pm and the meeting begins at 8pm. Supper is served after the talk and everyone is eligible for the night’s door prize. You do not need to be a member of the Society to attend, entry requiring a $2 door donation.